Tape technology remains the most cost effective backup solution to date for data archival. With current tape technology, tape media may have a lifetime of 30 years or more. However, writing data to tape media in a tape library can be a slow and time consuming process and may exceed the timeframe of a backup window for particular production system. In recent years, disk based backup has gained popularity due to a drop in disk prices and due a lesser need for manual intervention. The performance of disk based backup is generally consider faster and individual file restores from disk are significantly faster due to faster seek times.
A virtual tape library (VTL) is a disk based backup system which appears to the backup host as a real tape library system. Backup streams are however written to and restored from disk. The biggest advantage of a VTL over other disk based backup solutions is its seamless integration into an existing tape backup infrastructure. Backup applications, policies, licenses, etc. need not change due to a VTL emulating an existing tape library system.
VTLs may be used to “front-end” the tape system with a cache of disk drives, enabling backup data to be written to the cache very rapidly and allowing the production system to get back to work. Another advantage is that tape jobs may be “stacked” on the VTL, prior to writing the data to tape. This addressed a problem in mainframes that resulted in tape media being used very inefficiently, enabling write jobs to use the entire reel or cartridge rather than writing data in dribs and drabs across many pieces of media.
Once data is copied to the VTL disk, as an “off-line” or “near-line” process, the cached data can then be written to the tape system where it could be used to make local and off-site copies of the backup data. This multi-stage process can be used to eliminate “data friction,” the production latencies brought about by slow data copies.